1. Field of the Invention
This invention relates to a vacuum pump having an exhaust portion formed by a rotating blade portion and a stationary blade portion.
2. Description of the Related Art
In a vacuum pump such as a turbo-molecular pump, a rotor having rotating blade portions arranged in multiple stages is rotated at high speed in a pump container, and a gas molecule is moved from an intake port side to an exhaust port side by the rotating blade portions and stationary blade portions arranged between the stages of the rotating blade portions.
Each stage of the rotating blade portions has rotor blades, and each stage of the stationary blade portions has stator blades. The stationary blade portions are supported at predetermined intervals by spacers arranged on outer circumferences of the stationary blade portions. The stationary blade portions are formed into one ring shape by combining a pair of halved ring shape members.
The rotor blades and the stator blades are formed so as to be inclined with respect to a rotation surface of the rotor. A blade angle with respect to the rotation surface is generally formed so as to be larger on the upper stage side than the lower stage side.
As a method of manufacturing the stationary blade portions, there are a method of forming by mechanical working and a method of forming by plastic working. However, the method of manufacturing by the plastic working is advantageous in terms of cost. For example, the fiftieth paragraph of Japanese Unexamined Patent Application Publication No. 2005-105851 describes a procedure of manufacturing by the plastic working. This procedure includes:
(1) a step of preparing a disc plate made of metal such as aluminum, (2) a step of forming three cut lines on the disc plate along outlines of plural rows of blade portions (stator blades) by etching, and (3) a step of forming the blade portions by a predetermined inclination angle by pressing.
The above manufacturing method is to form the three cuts along outline shapes of the blade portions, and plastically deform the cut inner regions by the pressing, so as to form the blade portions by a predetermined blade angle. Outer circumferential side ends and inner circumferential side ends of the blade portions are isolated from the disc plate.
That is, there is no member for supporting the blade portions between the disc plate and the outer circumferential side ends of the blade portions, and between the disc plate and the inner circumferential side ends of the blade portions. Therefore, the blade portion, that is, the stator blades have small rigidity, and the blade angle of the stator blades is easily changed.